1. Field of the Invention
This invention relates to threaded tubular connections and more particularly to such connections employed in joining lengths of pipe or joints used for drilling oil and gas wells.
2. Background Description
Frequently, oil field tubular goods must be assembled and used under extremely adverse conditions. This is particularly true of tool joints used to join drill pipe, because in the normal course of drilling a well, the lengths of pipe or joints that comprise the drill string are assembled as the well is being drilled and are subjected to the many loads and vibrations of the drilling operations, disassembled as the drill string is temporarily withdrawn to change tools at the bottom of the drill string or while the partially drilled well is tested or for other purposes, and reassembled as the drill string is put back in operation.
Tool joints must be properly tightened to prescribed levels to achieve optimum performance and to resist additional rotational makeup while in service in the well. High operating torques applied to the drill string require even higher makeup torques during the assembly of the tool joints. Prior art tool joints utilize large shoulders adjacent to the threads to resist the loads caused by high makeup torques and to form pressure seals. The large shoulders require the outside diameter of the tool joint to be large.
Tapered wedge threads, are described in Reeves Reissue U.S. Pat. No. Re. 34,467, commonly assigned with the current application, are known to be an unusually strong connection that controls the stress and strain in the connected pin and box members to be within acceptable levels and is therefore employed in many heavy duty applications. However, the threads are generally dovetailed -(hyphen) shaped with load flanks and stab flanks that deverge outwardly to create crests of substantially wider dimensions than the contiguous roots. Such a-configuration creates an interlocking thread form. These wedge-type threads do not rely on shoulders to resist loads caused by torsional makeup. The conformation of the threads and adjoining shoulders have been used together in the prior art tool joints so that the bearing stresses that resist torsional makeup, the torque load and the sealing surfaces are shared between the threads themselves and the adjoining non-thread surfaces.
Dove-tailed threads such as Reeves that are symmetrical have a problem inasmuch as the slope of the stab flanks of a dovetailed thread pattern on a pin member present sharp edges to the similarly shaped sharp edges of the threads in the receiving box member as the two members are brought together to form a connection in the assembly process. Thus, unless the joints are perfectly axially aligned, the edges bang together, subjecting the edges to possible damage and preventing the pin from penetrating the box to the maximum extent. Likewise, upon disassembly, the sharp edges of the negative load flanks of the pin member and box member tend to hang onto one another as the joints are pulled apart, unless, again, the drilling rig that is employed to hold and manipulate a joint of the connection, usually the one with the pin member, can maintain perfect axial alignment of the pin member to the box member. The lack of perfect axial alignment can cause appreciable thread contact that can be injurious to the threads during stabbing or withdrawal, as the case may be.
There is mention in the resissue U.S. Pat. No. RE 34,467 that the threads discussed therein can also be semi-dovetailed in that one of the flank angles can be 90.degree. to the axis of the connection. It is also mentioned in U.S. Pat. Nos. 4,600,224 and 4,600,225, Blose, that a flank can be chevron-shaped or include a V notch. In the '224 patent the portion of the chevron load flanks nearest the thread root on the pin member are dovetailed with respect to the stab flanks and in the '225 patent the portion of the chevron load flanks nearest the thread root on the pin member are parallel with the stab flanks. Neither of these patents show threads similar to those disclosed herein. Moreover, none of the wedge threads employed in the prior art have all of the characteristics or advantages of the wedge threads herein disclosed and discussed.
Therefore, it is a feature of the present invention to provide an improved threaded tubular connection, especially for a drill pipe, using wedge threads, but wherein the flanks of the threads are slanted to minimize thread damage either during makeup or removal.
It is another feature of the present invention to provide an improved threaded connection, especially for a drill pipe, using wedge threads with novel interlocking generally dovetailed-shaped threads, wherein the threads totally engage to distribute all of the bearing stresses resisting torsional makeup, the torque load and sealing over the entire thread length.